Automotive vehicles are commonly equipped with various signal communication devices in the form of audio radios for receiving broadcast radio frequency (RF) signals, processing the RF signals, and broadcasting audio data (e.g., music) to passengers in the vehicle. Satellite digital audio radio (SDAR) services are available that offer digital radio service covering a large geographic area, such as North America. Currently, a couple of SDAR services are available in North America. One such SDAR service is referred to as Sirius satellite radio, which has three satellites in elliptical orbit. Another example of an SDAR service is XM satellite radio, which has two satellites in geo-stationary orbit. These SDAR services receive uplinked programming which, in turn, is rebroadcast directly to digital radios that subscribe to the service. Each subscriber to the SDAR service generally employs a digital radio having a receiver and an antenna for receiving the broadcast digital signals.
With SDAR service, the radio receivers are generally programmed to receive and decode the digital data signals, which typically include many channels of digital audio. In addition to broadcasting the encoded digital quality audio signals, the SDAR service may also transmit data that may be used for various other applications. For example, the broadcast signals may include data information for advertising, informing the driver of warranty issues, providing information about the broadcast audio information, and providing news, sports, and entertainment broadcasting, as well as other data information. Thus, the digital broadcast may be employed for any of a number of satellite audio radio, satellite television, satellite Internet, and various other consumer services.
Some SDAR services, such as Sirius satellite radio, use a time slicing technique to minimize the amount of data that is buffered in order to take advantage of an approximately four second memory buffer. One example of a conventional digital RF receiver system 100 is shown in FIG. 1 employing an antenna 112 and a digital RF receiver 114 providing an output to user input/output (I/O) device(s) 116. In the conventional receiver system 100, an RF tuner 118 generally provides certain select frequency signals to a digital demodulator 120 which separates the received signals from the various sources, such as first and second satellites, labelled SAT1 and SAT2, and a terrestrial transmission source labelled TERR. Signals from the sources SAT2 and TERR are processed by a maximum ratio combiner 124 and then are further processed by forward error correction circuitry 126 before passing onto the source decoder 128. The receiver 114 output is then made available to user I/O devices 116. Signals from the first source SAT1 may be temporarily stored (buffered) in a memory buffer 122 and the stored data may be read and combined with the signals from sources SAT2 and TERR in the maximum ratio combiner 124. The memory buffer 122 stores a cluster of data that may be made available in a buffered signal for correction of the signal broadcast in the forward error correction circuitry 126.
In some conventional systems, the receiver system typically buffers one cluster of data out of potentially multiple clusters of data that are transmitted. To take advantage of the maximum ratio combining, the cluster data is typically in the form of soft bits, i.e., the system buffers the I and Q data bits as a quantized signal, which is a digitized analog signal. The buffered signal can then be time aligned and combined with the other quantized signals.
In the Sirius satellite radio system, all the clusters are demodulated, however, the data clusters that are not used are generally dropped. While this approach works well for conventional receiver systems that provide either audio data or non-audio data only, it poses problems for systems that employ audio and non-audio data information from different clusters. Data clusters from multiple sources for such systems would require employment of separate digital chip sets to store both audio and non-audio data simultaneously which would result in added components (e.g., increased memory chip sets) and increased cost of the system.
It is therefore desirable to provide for an RF digital receiver that efficiently buffers data received from multiple sources. In particular, it is desirable to provide for a digital radio receiver that buffers audio data and other data information broadcast from multiple sources without requiring additional duplicative memory chip sets, thus providing a cost-effective approach to buffering data in a digital radio system.